A cable television network is primarily designed to distribute television signals from a central station to the homes of individual customers. In some networks the final link to the customer only conveys programmes which are actually being viewed and channel selection occurs at a switching point. However in all practical networks some links are required to convey the total output of the central station and these may be termed primary links.
A cable television network may also be arranged to convey other signals in addition to television programmes, for example digital codes for computers and stereo audio programmes. However, station operators are mainly concerned with having a sufficient number of video links on the assumption that these will provide the highest return on investment. It is therefore desirable to arrange the primary links as a collection of video channels each designed to convey a television signal.
The bandwidth of a video channel provides sufficient space for many frequency modulated (FM) audio signals each occupying approximately 53 kHz. However experiments have shown that a video channel producing the maximum tolerable amount of noise for good reception of television programmes produces too much noise for satisfactory reproduction of stereo audio signals. It is therefore an object of this invention to improve the quality of stereo audio signals transmitted in cable television systems.